(a) Field of the Invention
Generally, the present invention relates to a linear EMV actuator utilizing a permanent magnet and an electromagnet. More particularly, the linear EMV actuator operates to open and close an exhaust valve and an intake valve making valve operations linear so that the valve encounters a soft landing and active control of an amount of the opening of the valve.
(b) Description of the Related Art
Typically, a power generating apparatus, such as an engine, includes a valve and a device that opens and closes the valve. The valve typically functions to take air into a combustion chamber or for exhaust gas from the combustion chamber. Typically, a mechanical mechanism for driving the valve includes a crankshaft and a camshaft have been used to open and close the valve. More recently an EMV (Electro-Mechanical Valve train) valve driving method using electromagnetic operation has been developed as an alternative to the mechanical mechanism.
Two types of EMV actuators, an EMV using an electromagnet and an EMV actuator using a permanent magnet and an electromagnet are in use today.
The conventional EMV actuator that uses an electromagnet is described in Korean patent application No. 2002-0055972, and the conventional EMV actuator that uses a permanent magnet and an electromagnet is described in U.S. Pat. No. 4,779,582.
The EMV actuator using an electromagnet is configured such that a reciprocal motion of a valve is formed only by an electromagnet and a spring. That is, a first spring retainer is coupled to an upper portion of the valve and is supported by a valve spring. An armature is positioned at an upper end of the first spring retainer so as to be linearly movable. An upper coil and a lower coil are respectively disposed at an upper side and a lower side of the armature. A second spring retainer is connected to an upper portion of the armature while being elastically supported by an actuator spring. The EMV actuator using an electromagnet, current is alternately applied to the upper coil and the lower coil so that a driving force acts on the armature and thereby causes a vertically reciprocal movement of the valve.
The EMV actuator using a permanent magnet and an electromagnet together includes a valve stem and an armature that are integrally formed in order to produce a compulsory reciprocal motion of a valve. A permanent magnet is positioned outside the armature. In addition, an upper coil and a lower coil are respectively positioned above and below the permanent magnet. An actuator spring and a valve spring, for elastically supporting the armature are respectively positioned above and below the armature. Therefore, in the EMV actuator using a permanent magnet and an electromagnet, when current is alternately applied to the upper coil and the lower coil, a magnetic force is generated so that a position of the armature can be changed. Positive strengths of the actuator spring and the valve spring are similar to negative strengths due to the permanent magnet. Magnetic flux of the permanent magnet flows along the armature, the upper core, and the lower core. Since a negative strength due to the permanent magnet depending on a position of the armature increases as it approaches both ends, stable points of the armature are a center point and both end points.
That is, for an operation of the EMV actuator using a permanent magnet and an electromagnet, when the armature is position at one end, which is a stable point, current is applied to the opposite coil in order to move it to an opposite position. By repeating this, the armature can be reciprocally moved. Therefore, in the EMV using a permanent magnet and an electromagnet, current driving is needed only when a reciprocal motion is required in order to escape from stable points at both ends.
In the EMV actuator using only an electromagnet, since one valve is operated by respectively controlling two coils, i.e., upper and lower coils, there is a drawback in that many current controllers and displacement controllers are needed in the case where the engine has multiple cylinders. In addition, since an inductance and a magnetic force of a coil depending on a displacement of an armature are substantially nonlinear, a high-grade control strategy such as a nonlinear controller or an adaptive controller instead of a general linear controller is needed. In particular, great exertion is needed in order to realize a soft landing of a valve for avoiding problems cause by shocks on both ends of the valve. Furthermore, since initiation of movement is performed by using a resonance of a spring during initial driving of a valve, there are problems in that a time delay occurs and it is difficult to control an opening amount of a valve since the focus is on complete opening/closing of a valve.
In the EMV actuator using a permanent magnet and an electromagnet, since the strength of a spring and the negative strength of a permanent magnet are designed to be similar to each other, a substantial current is needed to obtain the speed of reciprocal motion of a valve that can be used in a real vehicle. In addition, in the EMV actuator using only an electromagnet, an upper coil and a lower coil are needed in order to control one valve, and there is a drawback of shocks on both ends of the valve. Further, although there is little problem in initial driving of a valve, it is difficult to freely control an opening amount of a valve, and although it has a better controllability than the EMV actuator using only an electromagnet, there is a drawback that controllability is limited because of a design of an actuator using nonlinearity.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.